1. Field of the Invention
The invention related to transmission of traffic information, and more particularly to a method and device for informing a user about the traffic situation in a traffic network.
2. Description of the Related Art
Information that is relevant for traffic is referred to hereinafter as "traffic information". Strictly speaking, this traffic information includes known bulletins concerning traffic backups, accidents, obstructions, etc. as well as measurements data such as speed or the quantity of vehicles which pass a measured cross section. But, in a broader sense, it also includes information about the surrounding environment such as weather information (freezing rain, fog) and restrictions (speed limits, non-resident limited access, prohibition against trucks, watershed areas, etc.). Information about tolls due or toll amounts also makes up a part of the traffic information in this context. Traffic information conventionally concerns route sections of a road network in particular. Also, general information (such as about fog) ultimately always relates to individual sections of road. Therefore, systems that are known and in use today reference the information to sections of road. A familiar example is verbal radio broadcast bulletins (e.g., "5-km backup on A3 between . . . and . . . "). There are also known systems which transmit these reports in code. In this case, for example in RDS/TMC, reference is made to a coded section of road.
First steps towards a quantitative integration of zone-related traffic information in traffic situation models have been proposed by the present Applicant, for example, in Patent Applications DE-P 195 26 148.8 and DE-P 196 50 844.4. The transmission of quantitative data measured in a point-by-point manner, in particular average speeds, is also known (WO 90/05959, Martell, et al.).
All of these methods have in common that the transmission of increasingly detailed information faces limitations in technical and ergonomic respects. On the technical side, the chief limiting factors are the available transmission bandwidth and communication costs; and on the ergonomic side, a large amount of extensively redundant information is transmitted or displayed because a characteristic (e.g., fog) can extend over many sections of road.
A further grave disadvantage of route section-oriented information consists in that both the traffic center and the receiver must have a common reference, i.e., a road section network known to both. If the center references the information as "4711", which defines a certain section of road, this reference must be known to the reception device for further processing, that is, the reception device must have or use the same "road map".
It is also practicable to reference a very limited partial network, especially a highway network (compare RDS/TMC). However, if this procedure is extended to the entire road network, the method, if it can be realized at all in technical respects, is very uneconomical. In particular, the problems of the common reference system also quickly become extremely complex when the entire road network must be maintained and updated in both the center and terminal device.